1. Field of the Invention
This invention relates generally to automatic gain controls (AG), and more particularly to a system and method of dual mode AGC for a digital radio receiver.
2. Description of the Prior Art
A digital radio broadcast system requires a radio frequency (RF) receiver having a high sensitivity and wide input dynamic range to cope with a wide range of RF input signal strengths. This requirement for a wide input dynamic range can only be met if the RF receiver has good linearity through the full RF receiver path over the required wide range of RF input signal strengths. The requirement to meet both high sensitivity and high linearity has been particularly problematic regarding RF receiver architectures and optimization.
In view of the foregoing, a need exists in the RF receiver art for an AGC architecture and method to optimize a digital radio receiver system such that it will achieve high input signal sensitivity and high linearity over a wide range of RF input signal strengths.
The present invention is directed to a system architecture and method of implementing dual mode automatic gain control for a digital radio receiver in order to achieve high input signal sensitivity and high linearity over a wide range of RF input signal strengths. The architecture most preferably comprises a complete integrated RF dual band receiver solution for digital audio broadcast (DAB). According to one embodiment, the dual band receiver system architecture includes a pair of dual band low noise amplifiers (LNA), three down converters, an IF gain controlled amplifier (GCA), a programmable gain amplifier (PGA), a 10-bit analog-to-digital converter (ADC), two voltage controlled oscillators (VCO), and two synthesizers. In order to accommodate a wide range input signal (i.e. xcx9cxe2x88x92100 dBm to xcx9cxe2x88x9210 dBm) at both band III and L-band antennas, the LNAs and the first down converter mixers are designed with a two-mode architecture capable of implementing both high and low gain mode control, depending upon the strength of the input signal.
Two AGC control algorithms are implemented within the system to ensure a high system linearity and to obtain an optimum system signal-to-noise ratio for a wide range (i.e. xcx9cxe2x88x92100 dBm to xcx9cxe2x88x9210 dBm) of input signals. The high/low gain mode switches of LNAs and mixers are controlled by a RF AGC, while a digital AGC controls the gain settings of the GCA and PGA to optimize the output signal to the requisite ADC input range.
As used herein, the following words have the following meanings. The words xe2x80x9cAlgorithmxe2x80x9d and xe2x80x9calgorithmicxe2x80x9d mean functions that can be implemented using either xe2x80x9chardwarexe2x80x9d or xe2x80x9csoftwarexe2x80x9d or a combination of both. The words xe2x80x9calgorithmic softwarexe2x80x9d mean an algorithmic program used to direct the processing of data by a computer or data processing device. The words xe2x80x9cdata processing devicexe2x80x9d as used herein refer to a CPU, DSP, microprocessor, micro-controller, or other like device and an interface system. The interface system provides access to the data processing device such that data could be entered and processed by the data processing device. The words xe2x80x9cdiscrete dataxe2x80x9d as used herein are interchangeable with xe2x80x9cdigitized dataxe2x80x9d and xe2x80x9cdigitized dataxe2x80x9d as used herein means data which are stored in the form of singularly isolated, discontinuous data or digits.